Polycarbonate has found many uses as an engineering thermoplastic because it combines, in general, a high level of heat resistance, impact resistance and dimensional stability with good insulating and non-corrosive properties, and it is easily molded. It does, however, suffer from a tendency to craze and crack under the effects of contact with organic solvents such as gasoline, especially when under a stress such as a flexural or torsional stress. Polycarbonate which has crazed is, undesirably, more likely to experience brittle rather than ductile failure from impact. This disadvantage has been somewhat relieved by the practice of blending polycarbonate with various olefin polymers such as polyethylene, polypropylene or polyisobutylene, as described for example in Goldblum, U.S. Pat. No. 3,431,224. These added substances are capable of improving the resistance of polycarbonate to solvents somewhat, but they tend to cause an offsetting increase in the delamination of the blended composition, as reported for example in Bussink, U.S. Pat. No. 4,122,131.
In U.S. Pat. No. 4,859,738, a solvent-resistant blend of polycarbonate, polyester and ethylene/carbon monoxide copolymer is disclosed. Also disclosed therein are several elastomeric impact modifiers which can be admixed with such a blend to improve its impact strength, and several additives for admixture therewith, including fillers. We have found that certain fillers when added to such a blend are preferred to others because they improve dimensional stability while preserving higher levels of the solvent resistance and impact strength which are imparted to polycarbonate by the polyester, ethylene/carbon monoxide and impact modifier.